#1568

Episode 1568
showing AM mod using a can oscillator
Be a Patron: / imsaiguy

[@landspide]

Love it if you could do something further on basic modulation technoques PSK, (g)FSK, OOK...

[@mikesradiorepair]

§15.219 is the rule that applies to most of those who use AM for microbroadcast as it calls for the maximum input power at the final radio frequency stage to be at or less than 100 milliwatts (0.1 watts) and the length of the antenna system (transmission line, radiator and ground) to not exceed 3 meters (10 feet).

[@tvelektron]

Try a magnetic loop antenna with this 3m of wire. Should result in a strong signal for Sure 😁

[@LousyPainter]

You produce some excellent videos. Always entertaining and educational. Good job! Looking forward to the next one. Thanks.

[@Hellhound604]

In the old days simplest method of AM modulation was to use a carbon-mic in series with the cathode of the oscillator-tube, but of course, getting hold of a carbon microphone is not that simple anymore

[@RideGasGas]

Have to comment on the final part of the video. One of the things I do in my day job is FCC licensing. This includes earth stations, satellites, and quite a few experimental licenses to support development and testing. The requirements for experimental licensing have changed from the old x milliwatts of power and 6 foot antenna. OET no longer has a minimum power value below which experimental licenses are not required. Pretty much you need to be in a faraday cage or anechoic chamber, otherwise they want you to get an experimental license. I would advise folks to get an amateur radio license. Then experimenting with equipment that operates within ham band limits and meets other technical requirements would be OK.

[@RideGasGas]

See: www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-5 See also FCC Dockets 10--236 and 06-155 for discussion on expanded opportunities for radio experimentation and market trials under Part 5.

[@aduedc]

You are not only AM modulating, but also FM modulating. This is evident with extra two side Spurs besides first spurs. In oscillators there is a concept called pushing, which changes in the supply causes FM modulation and they can model it using Basel function. This is significant in design of VCOs because the noise on the supply causes FM modulation and phase noise. You need to use some sort of multiplier after oscillator itself to AM modulate things.

[@nohrtillman8734]

I don’t see any amplitude delta…at all. It could be the frequency spectroscope is averaging the magnitude measurement of any given frequency, which would hide any rapid changes (modulation) I speculate what we see, and what we hear, is the ripple induced in the power input, not modulation of the carrier. This is what you suggested was happening. The center frequency is rock steady in amplitude and bandwidth, implying the oscillator does its job even with an unsteady input voltage. Very cool demonstration! Just not Amplitude Modulation of a signal like we think we’re seeing. Or, it’s been mis-labeled as amplitude modulation for a century.

[@Penfold42]

Good fun - was there a set of harmonics too ? I’m assuming it’s a square wave output

[@Travis141123]

CB guys listen up! AUDIO!!!

[@leetucker9938]

awesome

[@t1d100]

Excellent teaching. Helped me grok (understand) some things that I only kind of understood. Kewl. So, if a pepper wanted to DIY an automated SOS beacon, what frequency would they use?

[@IMSAIGuy]

Be a pepper: kzbin.info/www/bejne/oKemhZSZmKqeg6s

[@IMSAIGuy]

FCC rules: docs.fcc.gov/public/attachments/DOC-297510A1.pdf

[@markgreco1962]

@@IMSAIGuy😂😂😂😂

[@jameshall5835]

What is the near-field probe you are using. I use one that is a loop, but I like yours that you can just shove into a coil. Also what are those N-connected, screw connectors on the SA ?

[@IMSAIGuy]

kzbin.info/www/bejne/kHjFpWljn76Va5o

[@justin.campbell]

For SSB, do they just filter out one of the sidebands and amplify that instead?

[@IMSAIGuy]

that is one way. there are more complicated ways that also remove the carrier.

[@tonyfremont]

You might Google "doubly balanced mixer". In amateur radio they filter the undesired sideband and amplify what's left. This means a receiver has to regenerate the carrier either directly on the original carrier frequency for direct conversion, or by using a beat frequency oscillator that operates at an IF frequency. This converts the RF back to audio frequencies.

[@andrsam3682]

But why AM sidelobes apear in frequency domain? We a varying amplitude, but some carriers appear. I just don't get it

[@IMSAIGuy]

yes, that is where math helps. simplistically you have Fc (the carrier) and Fm (the modulation frequency). They combine to give Fc+Fm and Fc-Fm and the left over Fc To understand more I suggest reading about this and look at the math formulas for a modulated sine wave.

[@andrsam3682]

@@IMSAIGuy ok, I see. after multiplying we get the sum and the difference of our signals👍 do I understand right that second and other higher harmonics appear because of non-ideal modulation?

[@aduedc]

@@andrsam3682 Here we are not only AM modulating, but also FM modulating. This is evident with extra two side Spurs besides first spurs. In oscillators there is a concept called pushing, which the changes in the supply voltage causes FM modulation and they can model it using Basel function. This is significant in design of VCOs because the noise on the supply causes FM modulation and phase noise. To make a pure AM modulation you need to use some sort of multiplier after oscillator itself to get pure AM modulation. Search the internet for "VCO pushing" for more detail.

[@nohrtillman8734]

So this is not a demonstration of amplitude modulation. If so, then the center frequency would be changing in amplitude (voltage) and it is not. Unless the term “amplitude modulation” has been poorly named for a century.

[@andreaswaldherr5061]

@@IMSAIGuy But is "They combine to give Fc+Fm and Fc-Fm and the left over Fc" not frequency modulation? When you change the supply voltage very slowly (2:00) the amplitude of Fc changes, okay. But when the supply voltage changes quickly (3:45) the the sidebands appear. And also if you modulate with other electronics circuits. I have never find a explanation for this effect ( or one I understood :-)). Can someone help me (us) out here?

[@user-cf7be9km5m]

very sad but lately the subtitles disappeared somewhere already two weeks ago.

[@IMSAIGuy]

subtitles are working for me.

[@user-cf7be9km5m]

@@IMSAIGuy I understand. I lost the translation of your subtitles into another language. Looks like it's a youtube issue.

[@harshit9112]

How you make and connent antennaa

[@IMSAIGuy]

bend wire, solder wire. That is really a terrible antenna, just for fun on the video. it is not the correct length for that frequency

[@zerovolt24]

Hello, nice experiment. I've done something similar using a Colpitts oscillator and a function generator, showing the waveform on the oscilloscope (I don't have a spectrum analyzer). It's shown in this video: kzbin.info/www/bejne/joXHm5Zjjrmkfrc (the speech is in Italian but you can activate the translation of the text into English) Regards

[@QuintinMassey]

Sloppy explanation but ok demo.

[@tonyfremont]

Show us how it's done.

[@dixsusu]

Its fun . Now use an audio preamplfier for to hear sound too !